Precision machine vises are usually made of hardened steel with jaws of precision flat gripping surfaces, and are designed to exert great clamping force relative to their size on a gripped work piece. It is important that this great clamping force be applied as uniformly as possible over the entire gripping surfaces, and that there be minimum sidewise, lengthwise or vertical deflection of either jaw when the work piece is gripped.
Such precision machine vises may also be free standing for portable multiple use, or may be designed to be assembled on, or attached to, the machining table of a machine tool. Such machining table is typically made of hardened steel and has a perfectly flat upper surface containing a plurality of spaced parallel channels of inverted T-shape cross-section, conventionally called T-slots. When a vise is used with such machining tables, it is important that the vise not only be easy to assemble on the table, but also that it may be maintainable in a completely stationary position on the table while a gripped work piece is being machined.
The conventional type of precision machine vise utilizes a flat, relatively heavy base which houses a rotatable helically threaded shaft upon which a movable jaw is threaded. Rotation of this shaft causes the movable jaw to move on the base toward or away from a stationary jaw formed with or attached to one end of the base. The clamping force depends primarily upon the tightness of shaft rotation as well as the precision and ruggedness of the helical threads and accommodating grooves on the shaft and movable jaw. The clamping force is normally greatest in the region of the jaws adjacent the shaft, but becomes somewhat less in regions of the jaws remote from the shaft. In addition, this clamping force may suddenly reduce if the tightness of shaft rotation decreases due, for example, to vibration of the jaws during a machining operation.
The degree of jaw deflection depends to a considerable extent upon the amount of play in the bore of the base accommodating the rotatable shaft as well as in the grooves of the movable jaw accommodating the threads of the shaft. Over time, this deflection may become greater as the vise becomes worn and this play increases. Moreover, if this vise is used on a machining table, some auxiliary means must be provided for clamping the base of the vise in a completely stationary manner on the table.